The development of highly absorbent member, for use as disposable diapers, adult incontinence pads and briefs, and catamenial products such as sanitary napkins, are the subject of substantial commercial interest. A highly desired characteristic for such products is thinness. For example, thinner diapers are less bulky to wear, fit better under clothing, and are less noticeable. They are also more compact in the package, making the diapers easier for the consumer to carry and store. Compactness in packaging also results in reduced distribution costs for the manufacturer and distributor, including less shelf space required in the store per diaper unit.
The ability to provide thinner absorbent articles such as diapers has been contingent on the ability to develop relatively thin absorbent cores or structures that can acquire and store large quantities of discharged body liquids, in particular urine. In this regard, the use of certain absorbent polymers often referred to as "hydrogels," "superabsorbents" or "hydrocolloid" material has been particularly important. See, for example, U.S. Pat. No. 3,669,103 (Harper et al.), issued Jun. 13, 1972, and U.S. Pat. No. 3,670,731 (Harmon), issued Jun. 20, 1972, that disclose the use of such absorbent polymers (hereafter referred to as "hydrogel-forming absorbent polymers") in absorbent articles. Indeed, the development of thinner diapers has been the direct consequence of thinner absorbent cores that take advantage of the ability of these hydrogel-forming absorbent polymers to absorb large quantities of discharged body liquids, typically when used in combination with a fibrous matrix. See, for example, U.S. Pat. No. 4,673,402 (Weisman et al.), issued Jun. 16, 1987 and U.S. Pat. No. 4,935,022 (Lash et al.), issued Jun. 19, 1990, that disclose dual-layer core structures comprising a fibrous matrix and hydrogel-forming absorbent polymers useful in fashioning thin, compact, nonbulky diapers. See also, U.S. Pat. No. 5,562,646 (Goldman et al.), issued Oct. 8, 1996 and U.S. Pat. No. 5,599,335 (Goldman et al.), issued Feb. 4, 1997, both of which relate to absorbent cores comprising regions of high concentrations of hydrogel-forming polymer, where the polymer forms a gel-continuous liquid transportation zone upon swelling.
In addition to the use of hydrogel-forming absorbent polymers as the primary component in absorbent article storage structures, the use of polymeric foam materials derived from high internal phase water-in-oil emulsions ("HIPEs") has been identified. See, e.g., U.S. Pat. No. 5,260,345 (DesMarais et al.), issued Nov. 9, 1993, U.S. Pat. No. 5,387,207 (Dyer et al.) issued Feb. 7, 1995, and U.S. Pat. No. 5,560,222 (DesMarais et al.), issued Jul. 22, 1997. The foam materials, particularly those designed to function as liquid storage/redistribution components, provide several advantages over is storage structures comprising hydrogel-forming absorbent polymers in a fibrous matrix, including good wicking and liquid distribution characteristics, high storage capacity under pressure, flexibility, etc.
The primary focus of prior work in both the hydrogel-forming absorbent polymer and HIPE foam areas has been the maximization of liquid storage capacity in a relatively thin material. Hydrogel-forming absorbent polymer materials absorb liquid and provide a leakage protection and dryness in absorbent products. Once absorbed, the liquid in absorbent polymers is tightly held by osmotic forces, which helps prevent rewet of the topsheet by previously absorbed urine. However, hydrogel-forming polymer by itself has little ability to absorb liquid if the liquid is not delivered to its surface. This is especially critical at high capillary heights where the liquid is present only in small capillaries. For example, conventional softwood pulp exhibits almost no uptake at capillary suction heights of 100 cm. It is not surprising, then, that a mixture of pulp and hydrogel-forming polymer exhibits almost no uptake at 100 cm. Thus, in spite of the advancements made to achieve the goal of high liquid storage capacity in thin materials, there is a continuing need to provide high storage capacity materials that also exhibit high capillary suction capabilities. Storage materials which exhibit high capillary suction capacity will allow the dewatering of other absorbent core materials such as acquisition and distribution materials, one or both of which are typically included in absorbent cores of absorbent articles. By thoroughly dewatering these other absorbent core components, those materials will be better able to handle additional insults of liquid by the wearer. In addition to high capillary suction capacities in general, a particularly desirable property is the ability to provide such capacities at relatively high capillary suction heights. Movement of liquid from the discharge region (i.e., the crotch region of the article) to the front and rear of the article may provide enhanced wearer comfort when the article is wetted with liquid. As is clear, the ability of a storage material to dewater other core components, particularly the distribution material that wicks liquid to high capillary heights, is particularly relevant to their functioning as absorbent materials in absorbent articles.
Accordingly, it would be desirable to be able to provide a storage absorbent member having a high capillary suction capacity, wherein the storage absorbent member comprises hydrogel-forming absorbent polymer or another material that absorbs liquids primarily as a result of osmotic forces.